AWS Transit Gateway

Like a hub and spoke model
Single interface for all stuff to connect to
Can use it across multiple AWS accounts using RAM (Resource Access Manager)
Can use RTs to limit how VPCs talk to one another
Supports IP multicast

TGW Components

Attachments
TWG Maximum Transmission Unit (MTU)
Route table
Associations
Route propagation

TGW Evaluation Order

TGW takes preference in a particular order for same addresses that are advertised via different sources (e.g. VPN, direct connect)
For example, DX sources take preference over VPN